Encyclopedia of Microtonal Music Theory

triad

A chord of three tones none of which is an octave transposition of another.

The Major Triad in Just Intonation contains three tones whose frequency relations are 4:5:6 or 1/1 5/4 and 3/2.

The Minor Triad is 10:12:15 or 1/1 6/5 and 3/2.

Other triads such as the Septimal Minor 6:7:9 or 1/1 7/6 and 3/2 are used in extended Just Intonation tuning systems.

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[Joe Monzo]

"Common-practice" (classical) music-theory is based on triads, built upwards or downwards by stacking the various types of 3rds (intervals), resulting in 4 different types of triads. Below is a table showing the interval-string (is) for all 4 types and their inversions, in 12-edo tuning: